System and method for growing a plant in an at least partly conditioned environment

ABSTRACT

A system for growing a plant (1) in an at least partly conditioned environment includes a cultivation base (11) for receiving a culture substrate (3) with a root system (4) of the plant therein. Root temperature control elements (12) are provided which are able and adapted to impose a predetermined root temperature on the root system, and lighting elements (20,21,22) which are able and adapted to expose leaves of the plant to actinic artificial light. Leaf heating elements are also provided, which are able and adapted to impose on the leaf of the plant a leaf temperature varying from an ambient temperature. In a method for growing the plant a carbon dioxide assimilation management of a leaf system of the plant is thus influenced, and a supply of actinic light, the root temperature and the carbon dioxide assimilation management are adapted to each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 13/123,942 filed Apr.13, 2011, which is a National Stage Entry of International PatentApplication No. PCT/NL09/50617 filed Oct. 13, 2009, which claimspriority to NL Application No. 2002091 filed Oct. 13, 2008. Each of thepreviously noted applications is hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a system for growing a plant in an atleast partly conditioned environment, comprising a cultivation base forreceiving a culture substrate with a root system of the plant therein,root temperature control means which are able and adapted to impose apredetermined root temperature on the root system, and comprisinglighting means which are able and adapted to expose leaves of the plantto actinic artificial light. The invention moreover relates to a methodfor growing a plant in at least partly conditioned manner, whereinactinic light is supplied to the plant and wherein a root temperature ofa root system of the plant is maintained at a desired value.

Description of the Related Art

Such a system and such a method are applied on a significant scale inthe glass horticulture in greenhouses. An artificial climate is createdhere in an at least substantially closed and conditioned environmentbehind glass, and is adapted as far as possible to the optimal growthconditions of the plant for cultivating. It is hereby possible to growplants in areas and seasons in which the plant would not surviveoutdoors, or would at least not reach full development Furthermore, theproduction of the plant can thus be precisely adapted to a desiredharvesting time. It is thus possible to estimate relatively preciselybeforehand how much of which plant will be ready, and when. If desired,the same product can moreover be grown throughout the year and plantsand flowers at all stages of life can be cultivated.

In traditional glass horticulture sunlight is applied as the main sourceof actinic light, i.e. optionally visible light of a wavelength suchthat a plant response is thereby initiated or influenced, such as aphotosynthesis in the leaf or a determined mode of growth. Sunlightmoreover provides heat in the form of infrared radiation, whereby anincreased air temperature can be maintained in greenhouses relative toan outside temperature. In the absence of sunlight, such as particularlyat night, heating is possible in order to maintain such an increased airtemperature, while excessive entry of sunlight can be prevented duringthe day by means of partial blinding and filtering, and the climate canalso be regulated by means of ventilation. All in all, a climate in agreenhouse can thus be controlled within certain limits and can beadapted to a desired growth development of a plant for cultivation,which is further controlled by means of a controlled dosage of moistureand nutrients, in addition to pesticides. An additional component hereis the root temperature. It has been found that the growth of the plantcan be influenced by control of the root temperature. With a viewhereto, root temperature control means can be provided in order tomaintain a root temperature varying from the air temperature.

Classic glass horticulture does however also have drawbacks. Firstly,the environment must be particularly taken into account here. It costsenergy to keep a greenhouse warm and, for some plants, lighted day andnight. It is therefore important to regulate the energy management asefficiently as possible. Where greenhouses are built in or close todensely populated areas, the aspect of space is moreover an importantfactor. Traditional greenhouses do after all require entry of sunlightand take up a relatively large amount of expensive land area in theseareas, which could otherwise be employed for offices, house-building orinfrastructure. In order to address this problem, low-daylight, inparticular underground, daylight-free and multi-layer solutions arebeing sought in order to enable multiple use of the same land area.

Because not only heat but also actinic light will in such a case besupplied artificially, the energy management is even more of a problem,and there is therefore a need for a cultivation of plants which is asefficient as possible.

SUMMARY OF THE INVENTION

The present invention has for its object, among others, to provide asystem and method for growing a plant in an at least partly conditionedenvironment which enable a further improvement in efficiency.

In order to achieve the stated object, a system has the featureaccording to the invention that leaf heating means are provided, whichare able and adapted to impose on the leaf of the plant a leaftemperature varying from an ambient temperature. The system according tothe invention thus provides the option of a controlled evaporation andcarbon dioxide assimilation via the leaf by regulating a correct amountof energy on the leaf, in addition to a controlled lighting, both inrespect of the amount of light and in respect of spectral ratios, with aview to plant growth reactions, such as blue/red and red/far-red ratios,and in respect of light spectra necessary for specific reactions such aspigment formation, and in addition to a control and optimization of theroot pressure activity. This all takes place in an at least partlyconditioned environment in which the climate can be controlled withinnarrow limits in respect of, among other factors, an air humiditybalance, a room temperature and a carbon dioxide concentration as wellas water and nutrition for the plant.

The invention is based here on the insight that three factors areessentially responsible for a successful plant development, i.e. thephotosynthesis, the sap flow in the plant pushed upwards under theinfluence of a prevailing root pressure, and the carbon dioxideassimilation through mainly the leaf system of the plant, and that thesethree factors must at all times be adapted to each other in order toactually realize an optimal plant growth. In addition to the roottemperature and the entry of actinic light, a carbon dioxideassimilation management of the plant can also be controlled by providingthe leaf heating means in the system according to the invention. Due toadditional heating the stomata in the leaf will open further, soenhancing entry of carbon dioxide to the leaf and evaporation ofmoisture from the leaf. This latter is particularly important if a sapflow in the plant is stimulated by an increased root temperature, asthis flow will have to exit via the same stomata. Conversely, the leaftemperature can be decreased at a lower sap flow in order to preventundesired plant dessication. All in all, the most important climateparameters responsible for the development of the plant can thus becontrolled so that an optimal efficiency can be realized in each ofthese components with a minimal energy consumption.

A particular embodiment of the system has the feature according to theinvention that the lighting means are able and adapted to emit alighting spectrum which can be adapted to an intended photosynthesisand/or mode of growth of the plant to be cultivated. The actinic lightcomponents necessary for the development of the plant can thus besupplied only in precisely sufficient intensity, while non-actiniccomponents or an excess can be avoided as far as possible in order tolimit the overall energy consumption of the system and/or possibleharmful effect on the plant development.

In a further particular embodiment the system according to the inventionis characterized here in that the lighting means comprise a set oflight-emitting diodes, these diodes being able and adapted to emitradiation at different wavelengths and being individually controllable,optionally in groups. Such so-called LED elements produce substantiallymonochromatic light and are obtainable for different wavelengths,particularly in the far-red, yellow, green and blue visible part of thespectrum. A photosynthetically active (PAR) spectrum which best suitsthe concrete needs of the plant can thus be constructed, and optionallymodified, by combination and selection of individual LEDs.

The leaf heating means can be formed per se in various ways, although ina preferred embodiment the system according to the invention ischaracterized in that the leaf heating means comprise at least one heatsource able and adapted to irradiate the leaf with infrared radiation.Other than heating means which, wholly or partially through guiding ofan intervening medium, are capable of heat-exchanging contact with theleaf, such a heat source enters into heat-exchanging contact mainlythrough direct irradiation. Not only does this result in a highlyeffective and efficient heating of the leaf system, the intendedtemperature difference with the environment contributing toward adesired widening of the stomata is hereby also achieved in particularlyeffective manner. In a further preferred embodiment the system accordingto the invention is characterized here in that the lighting means andthe heat source are accommodated in mutually separated fittings in orderto thus exclude a possibly disruptive influence of an inevitable heatdissipation in the heat source itself from the conditioning sphere ofthe actinic light source. Although the root temperature control meansper se can also be realized in diverse ways, a preferred embodiment ofthe system according to the invention has the feature that the roottemperature control means comprise a closed conduit system for receivingtherein during operation a liquid flow with a controlled temperature,wherein the conduit system is able and adapted to enter intoheat-exchanging contact with the culture substrate. Such a conduitsystem can for instance be formed by a system of tubes or fins in orunder the culture substrate, in which a liquid flow meandersaltematingly. The root temperature can be uniformly controlled by thusheating or cooling the culture substrate in which the root system isreceived. A further embodiment of the system according to the inventionhas the feature here that a control is provided between the leaf heatingmeans and root temperature control means which imposes a mutualdependence on the leaf temperature and the root temperature. In forinstance a normal growth trajectory the leaf temperature will thusfollow, optionally in directly proportional manner, a change in roottemperature so that the assimilation management keeps pace with avariation in the root pressure.

In order to achieve the stated object, a method has the featureaccording to the invention that a carbon dioxide assimilation managementof a leaf system of the plant is also influenced, and that a supply ofactinic light, the root temperature and the carbon dioxide assimilationmanagement are adapted to each other. This method is in line with theabove described insight that the root temperature, the supplied lightspectrum and the carbon dioxide assimilation management of the leaf arenot separate entities but will only arrive at the optimal result inmutual relation. The method according to the invention provides theoption of arranging this mutual relation in the form of for instance aplant-dependent and/or growth phase-dependent modification of thesegrowth factors.

In a particular embodiment the method according to the invention ischaracterized in that the carbon dioxide assimilation management isinfluenced by regulating a leaf temperature of the leaf system so thatit differs from an ambient temperature. The above described systemaccording to the invention is highly suitable for an implementation ofthis method in that the leaf temperature can hereby be regulated sothat, if desired, it differs from the environment, in addition to acontrol of the other stated growth factors. In a further particularembodiment the method according to the invention is characterized herein that the supply of light, the root temperature and the leaftemperature are adapted to each other depending on the plant.

For the purpose of an optimal photosynthesis and mode of growth of theplant, a further particular embodiment of the method according to theinvention has the feature that actinic artificial light is supplied witha spectrum adapted to an intended photosynthesis and/or mode of growthof the plant. By thus specifically adapting the mutual ratio andintensity of the various light components which play a part in thephotosynthesis and growth development of the plant, a high yield cannevertheless be realized at a relatively low total light intensity andenergy consumption. Within the context of the present invention afurther particular embodiment of the method according to the inventionhas the feature here that the artificial light spectrum, a leaftemperature of the leaf and the root temperature are controlledindividually of each other but in mutual relation, depending on theplant.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will now be further elucidated on the basis of anexemplary embodiment and an accompanying drawing. In the drawing:

FIG. 1 shows a cross-sectional partial view of a device in an exemplaryembodiment of a system according to the invention.

The FIGURE is otherwise purely schematic and not drawn to scale. Somedimensions in particular may be exaggerated to greater or lesser extentfor the sake of clarity. Corresponding parts are designated as far aspossible in the FIGURE with the same reference numeral.

DETAILED DESCRIPTION OF THE INVENTION

The system shown in FIG. 1 makes use of a multi-layer cultivation ofplant 1 so as to enable the best possible use of an available surfacearea. The plant is accommodated here in culture trays 2 with a suitableculture substrate 3 therein, such as earth, glass wool, rockwool orsimply water, for the purpose of receiving a root system 4 of the planttherein. Culture trays 2 are placed one above the other on beams 11 of aframe 10 constructed almost entirely from stainless steel. Any desirednumber of such carriages 10 can thus be combined to form a completecultivation system in a conditioned environment, wherein the plant isbrought to full development in fully controlled manner. Irrigation andfertilizing provisions (not further shown) are arranged at or incarriages 10 in order to provide the plant with sufficient water and thenecessary nutrients.

Beams 11 of the carriages each comprise a closed conduit system 12 of ahose or tube which meanders at a regular pitch. In this respect a systemof successive hollow fins can optionally also be applied as conduitsystem. This conduit system 12, through which a heat-carrying mediumsuch as water of a controlled temperature can be guided in order tocontrol a temperature of the root system, forms part of root temperaturecontrol means. The heated medium relinquishes heat during operation tofor instance the beams, which in turn conduct the heat via the culturetrays to the culture substrate with the root system of the planttherein. Conversely, heat can also be extracted from the root bed bymeans of a cooled heat-carrying medium. The root system is thus keptmore or less precisely at a desired root temperature during operationaccording to the method described here. In order to give this heattransport a more specific control, and thereby a more efficientheat-exchanging capacity, the beams take a multi-layer form with aninsulating base 13 of foamed plastic such as polyurethane foam orpolystyrene foam, with a reflective top layer 14, for instance areflective metal coating or an additional intermediate layer providedwith such a coating, followed by conduit system 12 and thereon a metalplate 15, for instance of stainless steel, having good thermalconductivity.

Each layer of cultivation system 10 is provided with an artificial lightsource 20 in the form of a light fitting having therein groups 21 oflight-emitting diodes (LEDs), in addition to possible other lightsources 22 such as ultraviolet or infrared radiators. The LED diodes inthe first groups emit light at least mainly in the visible part of thespectrum, in particular red, yellow, green or blue light, while thesecond groups 22 add invisible components such as infrared light andnear-ultraviolet light thereto. Light fittings 20 are provided with acontrol (not further shown) with which the different groups and theelements within the groups can be controlled selectively andindividually in order during operation to then adapt a specific spectralcomposition of the emitted light to the requirements and type of theplant 1 being cultivated. Because the beams are optically separated fromeach other to a significant extent, a different spectrum can if desiredthus be supplied per beam in order to thus cultivate different plants incombination with each other and provide each with an optimal spectrum.The system is highly suitable here for application in a low-daylight oreven daylight-free environment, such as for instance in an undergroundsituation.

Further provided in the cultivation system are leaf heating means 30 inthe form of infrared radiators which are disposed in layers on eitherside on the shelves of the carriages. The infrared radiators emit directheat radiation in the direction of the leaf of the plant and thus, ifdesired, increase a leaf temperature of the leaf relative to the ambienttemperature. The carbon dioxide assimilation management of the leaf canthus be controlled to a significant degree and particularly be adaptedto the root pressure of the sap flow in the plant which is produced byroot system 4. This because heating of the leaf results in a widening ofthe stomata in the leaf, whereby they will be better able to relievesurplus root pressure by allowing water to evaporate, while a sufficientcarbon dioxide assimilation required for the photosynthesis, which is inturn activated and controlled using the lighting means, neverthelesscontinues via these same stomata. If on the other hand cuttings of theplant are taken, the leaf system is however not heated, or at leastheated less, at an increased root simulation so as to thus limitevaporation and ensure an excess of moisture on the cutting surface. Allin all, the main growth factors, i.e. the photosynthesis, the rootpressure and the carbon dioxide assimilation, can thus be regulatedindividually in the system according to the invention, and these factorsare precisely adapted in mutual relation at each stage of growth and foreach plant in order to enhance optimum growth and mode of growth.

Although the invention has been further elucidated above on the basis ofonly a single exemplary embodiment, it will be apparent that theinvention is by no means limited thereto. On the contrary, many othervariations and embodiments are possible without requiring a skilledperson to depart from the scope of the invention in a manner which isless obvious. The root temperature control means can thus also comprisea conduit system directly in the culture substrate which is in more orless direct heat-exchanging contact with the root system. In the case ofcultivation on water or a watery substrate, such as glass wool orrockwool, the root temperature can also be controlled by a controlledcontrol of the temperature of the water supplied thereto.

Use is made in the example of artificial light by means oflight-emitting diodes (LEDs), although within the scope of the inventionconventional incandescent growing lamps are also suitable instead, andthe invention can also be applied in full or partial daylight.

Use is made in the given example of multi-layer cultivation on mobilecarriages, although cultivation in a single layer and/or cultivation ina fixed arrangement can also be envisaged within the scope of theinvention.

Within the scope of the invention the carbon dioxide assimilation andmoisture evaporation via the leaf system can be controlled and adaptedto particularly the root pressure. Instead of by means of directinfrared lamps, this can also be achieved by means of spiral filaments,heat panels or the like disposed close to the leaf system. If desired,the leaf heating means, such as the infrared radiators in the example,can further be integrated in the same fitting as the artificial lightingmeans, for instance for the purpose of saving space and/or ease ofinstallation.

What is really important in the invention is that the growth developmentof the plant is determined by the weakest link in a chain of the mostimportant growth factors, i.e. photosynthesis, root pressure and carbondioxide assimilation, and that all these factors are controlled inmutual relation according to the invention and, if desired, areartificially modified in order to realize an optimal chain.

1. System for growing a plant in a daylight-free environment, in whichsaid environment is at least partly conditioned, comprising acultivation base for receiving a culture substrate with a root system ofthe plant therein, wherein an artificial light source is able andadapted to expose leaves of the plant to actinic artificial light,wherein root temperature control means are provided in said environmentwhich are able and adapted to control a root temperature of the rootsystem, wherein leaf heating means are provided in said environmentwhich are able and adapted to impose on the leaf of the plant a leaftemperature that differs from an ambient temperature, and wherein saidartificial light source, said root temperature control means and saidleaf heating means are collectively controlled and individuallyadjustable in dependence of one another.
 2. System as claimed in claim1, wherein the artificial light source is configured to emit a lightingspectrum which can be adapted to an intended photosynthesis and/or modeof growth of the plant to be cultivated.
 3. System as claimed in claim2, wherein the artificial light source comprises a set of light-emittingdiodes, said diodes being configured to emit radiation at differentwavelengths and being individually controllable, optionally in groups.4. System as claimed in claim 1, wherein the leaf heating means compriseat least one heat source configured to irradiate the leaf with infraredradiation.
 5. System as claimed in claim 4, wherein the artificial lightsource and the leaf heating means are accommodated in mutually separatedfittings.
 6. System as claimed in claim 1, wherein the root temperaturecontrol means comprise a closed conduit system for receiving thereinduring operation a liquid flow with a controlled temperature, whereinthe conduit system is configured to enter into heat-exchanging contactwith the culture substrate.
 7. System as claimed in claim 1, wherein acontrol is provided between the leaf heating means and root temperaturecontrol means which imposes a mutual dependence on the leaf temperatureand the root temperature, wherein a change of one of said leaftemperature and said root temperature results in a change a another ofsaid leaf temperature and the root temperature in a defined proportion.8. Method for growing a plant in at least partly conditioned manner,wherein actinic light is supplied to the plant by means of an artificiallight source in a daylight-free environment, wherein a root temperatureof a root system of the plant is maintained at a desired value by meansof root temperature control means, wherein a carbon dioxide assimilationmanagement of a leaf system of the plant is influenced by regulating aleaf temperature of the leaf system by means of leaf heating means sothat said leaf temperature differs from an ambient temperature, andwherein the artificial light source, the root temperature control meansand the leaf heating means are collectively controlled thereby adaptinga supply of actinic light, the root temperature and the carbon dioxideassimilation management to one another.
 9. Method as claimed in claim 8,wherein the supply of light, the root temperature and the leaftemperature are adapted to each other depending on the plant.
 10. Methodas claimed in claim 9, wherein said actinic artificial light is suppliedwith an artificial light spectrum adapted to an intended photosynthesisand/or mode of growth of the plant.
 11. Method as claimed in claim 10,wherein the artificial light spectrum, the leaf temperature of the leafand the root temperature are controlled collectively in mutual relation,depending on the plant, and wherein a change in one of the artificiallight spectrum, the leaf temperature and the root temperature results ina change one other of the artificial light spectrum, the leaftemperature and the root temperature.